Forge welding involves circumferential heating of pipe ends and subsequent metallurgical bonding of the heated pipe ends.
A large variety of heating technologies may be used to make the pipe ends hot enough such that the metallurgical bond can be made. The heating techniques may involve electric, electromagnetic, induction, infrared, arcing and/or friction heating or combinations of these and/or other heating methods.
When used in this specification the term forge welding is intended to encompass all techniques which involve circumferential heating of pipe ends and subsequent metallurgical bonding the heated pipe ends, including welding techniques that are generally known as fusion welding, friction welding, flash welding and/or butt welding.
It is known from U.S. Pat. Nos. 4,566,625; 4,736,084; 4,669,650 and 5,721,413 issued to Per H. Moe that it may be beneficial to flush the pipe ends just before and during the forge welding operation with a reducing flushing gas, such as hydrogen or carbon monoxide, such that any oxygen skin is removed from the heated pipe ends and a metallurgical bond with a minimal amount of irregularities is obtained. It is also known from U.S. Pat. Nos. 2,719,207 and 4,728,760 to use non explosive mixtures comprising about 95% by volume of a substantially insert gas, such as argon, nitrogen and/or helium, and about 5% by volume of a reducing gas, such as hydrogen and/or carbon monoxide for flash welding and induction butt welding.